Let-7d-5p improves mouse cognitive function by targeting bach1 in Alzheimer's disease

MicroRNAs (miRNAs) have emerged as critical modulators in Alzheimer's disease (AD) pathogenesis. The lethal-7 (let-7) family functions as key regulators of cell apoptosis, differentiation, and immune response. Herein, we explore the functions and underlying mechanisms of let-7d-5p in AD progression.

Eight-month-old male APP/PS1 transgenic mice and wild-type C57BL/6 J mice were assigned to the model and control groups, respectively. Model mice received intrahippocampal injections of either a negative control adenovirus (Ad-NC) or a let-7d-5p overexpression adenovirus (Ad-let-7d-5p). The Morris water maze test was conducted to assess cognitive function. Hippocampal histopathological changes were evaluated using hematoxylin and eosin staining. Aβ deposition was detected via immunohistochemical staining. SH-SY5Y cells were transfected with let-7d-5p mimics prior to treatment with 10 μM Aβ_1-42. Cell viability and apoptosis were examined using MTT assays and flow cytometry. The expression levels of let-7d-5p and bach1 were measured using RT-qPCR. Western blotting was conducted to evaluate bach1, Bcl-2, and cleaved caspase-3 protein levels. The binding relationship between let-7d-5p and bach1 was verified using luciferase reporter assays.

In vitro, Aβ_1-42 treatment induced the downregulation of let-7d-5p and decrease of cell viability. However, overexpression of let-7d-5p significantly increased let-7d-5p level, enhanced cell viability and inhibited cell apoptosis of Aβ_1-42-treated SH-SY5Y cells. Moreover, overexpression of let-7d-5p upregulated Bcl-2 protein levels and downregulated cleaved caspase-3 protein levels in Aβ_1-42-treated SH-SY5Y cells. Furthermore, let-7d-5p overexpression ameliorated oxidative stress injury in Aβ_1-42-treated SH-SY5Y cells. Importantly, bach1 upregulation counteracted the inhibitory effects of let-7d-5p overexpression on Aβ_1-42-induced cellular injury. In vivo, let-7d-5p overexpression mitigated cognitive deficits of AD mice, as indicated by reduced escape latency and increased platform crossings. Additionally, let-7d-5p overexpression attenuated hippocampal histopathological changes and Aβ deposition in APP/PS1 mice. At the molecular level, let-7d-5p targeted bach1 3'UTR and repressed its mRNA and protein expression in vitro and in vivo. Rescue assays further validated that bach1 overexpression restored the protective effect of let-7d-5p on cognitive deficits and pathological injuries.

Let-7d-5p alleviates cognitive deficits in AD by inhibiting Aβ deposition and neuronal apoptosis through targeting bach1.